How to Break Down a PRD for Claude Code Development
I handed my 30-page PRD to Claude Code and said “implement everything.”
It failed spectacularly. The code was inconsistent, the architecture didn’t match, and half the features were built on top of decisions that made no sense.
Here’s what I learned about making PRDs work with AI coding assistants.
The Problem: PRDs Are Written for Humans, Not AI
When you give Claude Code a complete PRD, several things go wrong at once:
┌─────────────────────────────────────────────────────────┐│ 30-page PRD ││ ┌─────────────────────────────────────────────────┐ ││ │ Business Requirements (high-level, ambiguous) │ ││ │ User Stories (human language, no tech specs) │ ││ │ Acceptance Criteria (open to interpretation) │ ││ │ Dependencies (implicit, not ordered) │ ││ └─────────────────────────────────────────────────┘ ││ ↓ ││ Claude Code ││ ↓ ││ ┌─────────────────────────────────────────────────┐ ││ │ Context overload, missing technical details, │ ││ │ wrong interpretation cascade, no clear order │ ││ └─────────────────────────────────────────────────┘ │└─────────────────────────────────────────────────────────┘PRDs contain business-level language that’s open to interpretation. They rarely specify exact data structures, API contracts, or implementation patterns. They don’t tell Claude Code which dependencies need to be built first.
One wrong interpretation early corrupts the entire implementation.
The Solution: Break It Down Before Building
I changed my approach. Instead of handing over the full PRD, I now follow a three-step process:
PRD → Spec Documents → Vertical Slices → Incremental ImplementationStep 1: Create Spec Documents
I transform my PRD into AI-friendly specifications:
## Foundation Requirements
Tech Stack:- Python 3.11 with Flask- PostgreSQL database- SQLAlchemy ORM- Alpine.js + Tailwind for frontend
Database Schema:- users table (id, email, password_hash, created_at)- tasks table (id, user_id, title, status, created_at)
API Patterns:- REST endpoints returning JSON- JWT authentication- Error format: {"success": false, "error": "message"}A spec document is concrete. No business abstractions. Technical details only.
## Feature: Create Task
User Story: As a logged-in user, I want to create a task with a title.
Technical Implementation:- POST /api/tasks- Request body: {"title": "string"}- Validation: title required, 1-200 characters- Response: {"success": true, "data": {"id": 1, "title": "...", "status": "pending"}}
Dependencies:- Requires users table (foundation)- Requires JWT middleware (foundation)
Files to create:- backend/routes/tasks.py (endpoint)- backend/models/task.py (entity)- frontend/components/TaskForm.js (form)- tests/test_task_create.py (tests)Notice the difference? This tells Claude Code exactly what to build.
Step 2: Break Into Vertical Slices
Each slice is a complete, testable feature. Not horizontal layers.
Phase 1: Build ALL entities (users, tasks, projects, comments...)Phase 2: Build ALL repositoriesPhase 3: Build ALL endpointsPhase 4: Build ALL frontend componentsPhase 5: Build ALL tests
Problem: Nothing works until Phase 5. Errors compound.Slice 1: User registration ├── backend entity ├── backend repository ├── backend endpoint ├── frontend form └── tests (all pass)
Slice 2: Task creation ├── backend entity ├── backend repository ├── backend endpoint ├── frontend form └── tests (all pass)
Slice 3: Task listing └── ... (complete vertical)Each slice works end-to-end. I can test it. I can verify it. If something breaks, I know exactly where.
Step 3: Implement in Phases
I organize my vertical slices into phases:
Phase 1: Foundation (no PRD needed, standard patterns) ├── Database setup ├── Core entities ├── Base repository pattern ├── Authentication middleware └── Logging setup
Phase 2: Core Features (vertical slices from PRD) ├── Feature A (full vertical) ├── Feature B (full vertical) └── Feature C (full vertical)
Phase 3: Polish ├── Error handling ├── Edge cases ├── Performance optimization └── DocumentationWhy This Works Better
| Problem | Old Approach | New Approach |
|---|---|---|
| Context overload | 30 pages at once | 2 pages per slice |
| Ambiguity | Business language | Technical specs |
| Missing details | Claude guesses | Explicit in spec |
| Wrong ordering | Claude decides | I define phases |
| Error cascade | Corrupts everything | Contained to slice |
When Claude Code works on one vertical slice with a clear spec, it produces consistent, correct code.
Common Mistakes I Made
| Mistake | Why It Fails | Better Approach |
|---|---|---|
| ”Implement all entities first” | Horizontal coupling, no testing until end | One entity with its full vertical slice |
| ”Here’s my 50-page PRD” | Context dilution, inconsistent decisions | Create 2-page specs per feature |
| ”Build backend, then frontend” | No end-to-end validation until end | Complete vertical slices incrementally |
| ”Add these 10 features” | Claude loses track of priorities | One feature at a time with clear specs |
| No spec document | Claude interprets loosely | Precise technical specifications first |
My Workflow Now
1. Write PRD (human language, business context) ↓2. Create spec documents (technical language, implementation details) - spec-foundation.md - spec-feature-A.md - spec-feature-B.md ↓3. Phase 1: Implement foundation - Give Claude Code spec-foundation.md - Run tests, verify everything works ↓4. Phase 2: Implement features one by one - Give Claude Code spec-feature-A.md + spec-foundation.md - Run tests, verify slice works end-to-end - Repeat for each feature ↓5. Phase 3: Polish - Give Claude Code specific polish tasksI never give Claude Code more than 2-3 spec documents at once. Each spec is 1-2 pages maximum.
Summary
In this post, I showed how to break down a PRD for Claude Code development. The key point is translating human-oriented requirements into AI-friendly specifications, then implementing one vertical slice at a time.
The translation step matters. PRDs are for humans. Specs are for AI. Don’t skip this step.
Final Words + More Resources
My intention with this article was to help others share my knowledge and experience. If you want to contact me, you can contact by email: Email me
Here are also the most important links from this article along with some further resources that will help you in this scope:
Oh, and if you found these resources useful, don’t forget to support me by starring the repo on GitHub!
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